Bearing unit for wheel and manufacturing method thereof

ABSTRACT

A bearing unit for a wheel has a rotary ring whose raceway surface is hardened by a thermal process. In this bearing unit, the side surface of a fitting flange for fixedly joining a rotary body for braking and a wheel, is formed by working in a predetermined configuration after the raceway surface of the rotary ring has been subjected to the thermal process. The raceway surface of the rotary ring is worked in a predetermined configuration and dimensions on the basis of the side surface of said fitting flange. This bearing unit can restrain disagreeable noises and vibration from being caused upon braking.

This application is a continuation of application Ser. No. 09/505,190,filed Feb. 16, 2000 now U.S. Pat. No. 6,523,909.

This application claims the benefits of Japanese Application Nos.11-038329 and 11-372393 which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an improvement of a bearing unit forsupporting a wheel of an automobile as well as a rotary body for brakingsuch as a rotor or a drum, and to an improvement of a method ofmanufacturing such bearing unit for the wheel.

2. Related Background Art

A wheel 1 constituting a traveling wheel of an automobile and a rotor 2constituting a disk brake classified as a braking device, are rotatablysupported by a knuckle 3 as a component of a suspension on the basis of,for example, a structure shown in FIG. 4. To be more specific, acircular support hole 4 is formed in the knuckle 3. An outer ring 6defined as a static ring constituting a bearing unit 5 for a wheel, towhich the present invention is applied, is fixed to within the supporthole 4 a by use of a plurality of bolts 7. On the other hand, the wheel1 and the rotor 2 are fixedly joined through a plurality of studs 9 anda plurality of nuts 10 to a hub 8 as a component of the wheel bearingunit 5.

Outer ring double raceways 11 a, 11 b each serving as a static-sideraceway surface are formed in an inner peripheral surface of the outerring 6, and a joint flange 12 is provided on an outer peripheral surfacethereof. The thus configured outer ring 6 is fixed to the knuckle 3 byjoining the joint flange 12 to the knuckle 3 with the bolts 7.

By contrast, a fitting flange 13 is provided at a portion protrudingfrom an aperture of an outer side end (the term “outer or external”implies an outside portion in a widthwise direction in a state of beingassembled to the automobile, i.e., the left side in each drawing. Incontrast, the term “inner or internal” implies a central portion in thewidthwise direction in the state of being assembled to the automobile,viz., the right side in each of the components.) of the outer ring 6.The wheel 1 and the rotor 2 are fixedly joined through the studs 9 andthe nuts 10 to one single surface (an external surface in theillustrated example) of the fitting flange. Further, an inner ringraceway 14 a is formed in a portion, facing to the more external raceway11 a of the outer ring double raceways 11 a, 11 b, of the outerperipheral surface of the intermediate portion of the hub 8. Moreover,the inner ring 16 is fixedly fitted onto a small-diameter steppedportion 15 provided at an inner side end of the hub 8. Then, the innerring raceway 14 b formed in the outer peripheral surface of the innerring 16 is disposed facing to the more internal raceway 11 b of theouter ring double raceways 11 a, 11 b.

Balls 17, 17 each defined as a rolling member are provided in a rollablemanner by pluralities between the outer ring raceways 11 a, 11 b and theinner ring raceways 14 a, 14 b in a state of being held by retainers 18,18. Based on this construction, a double-row angular ball bearing with aback face combination is structured, the hub 8 is rotatably supported inthe outer ring 6, and a radial load and a thrust load are supported in asustainable manner. Note that seal rings 19 a, 19 b are provided betweeninner peripheral surfaces of two side ends of the outer ring 6, an outerperipheral surface of an intermediate portion of the hub 8 and an outerperipheral surface of an inner side end of the inner ring 16, thuscutting off a space accommodating the balls 17, 17 from the outsidespace. Further, in the illustrated example, the wheel bearing unit 5 isstructured for a drive wheel (corresponding to a rear wheel of a FR carand an RR car, a front wheel of an FF car, and whole wheels of a 4WDcar), and hence a central portion of the hub 8 is formed with a splinehole 20. Then, a spline shaft 22 of a constant velocity joint 21 isinserted into the spline hole 20.

When using the roll bearing unit 5 for the wheel described above, asshown in FIG. 4, the outer ring 6 is fixed to the knuckle 3, and therotor 2 and the wheel 1 assembled with an unillustrated tire are fixedto the fitting flange 13 of the hub 8. Further, the rotor 2 of thosecomponents is combined with an unillustrated support and anunillustrated caliper which are fixed to the knuckle 3, thusconstituting a disk brake for braking. When braking, a pair of padsprovided with the rotor being interposed therebetween are pressedagainst the two side surfaces of the rotor 2.

It is a known fact that vibrations called judder followed bydisagreeable or annoying noises often occur when braking the wheels ofthe automobile. One of a variety of known causes of those vibrations maybe an ununiform state of frictions between the side surface of the rotor2 and the lining of the pad, however, deflections of the rotor 2 arealso known as another large cause. More specifically, the side surfaceof the rotor 2 should be fundamentally right-angled to a rotationalcenter of the rotor 2, however, a perfect perpendicularity is hard toobtain due to an inevitable manufacturing error. As a result, the sidesurface of the rotor 2 inevitably deflects more or less in directions ofthe rotational axis (right and left directions in FIG. 4) when theautomobile travels. If such deflections (displacement quantities in theright and left directions in FIG. 4) increase, and if the linings of thepair of pads are pressed against the two side surfaces of the rotor 2for braking, the judder occurs. Then, the contact between both surfacesof the rotor 2 and the respective linings of the pad becomesnon-uniformed, wherein a partial abrasion of the linings is caused.

It is of much importance for restraining the judder occurred by suchcauses to decrease (axial) deflections of the side surface of the rotor2 (to enhance the perpendicularity of the side surface to the centralaxis of rotation). Then, it is required that a perpendicularity of afitting surface (one side surface of the fitting flange 13) of thefitting flange 13 to the rotational center of the hub 8 and a surfaceaccuracy of the fitting surface itself be enhanced for restraining thosedeflections. Factors for exerting influences upon the perpendicularityand the surface accuracy might exist by pluralities, however, thefactors having an especially large influence may be a parallelismbetween the fitting surface and the raceway surface (between the outerring raceways 11 a, 11 b and the inner ring raceways 14 a, 14 b) withrespect to the perpendicularity, and a thermal process deformation withrespect to the surface accuracy. Further, for enhancing the parallelismof those factors, among the constructive elements of the hub 8, theremust be a necessity for setting highly accurately a positionalrelationship between the one side surface of the fitting flange 13, theinner ring raceway 14 a formed in the outer peripheral surface of theintermediate portion and the small-diameter stepped portion 15 providedat the inner side end, and configurations and dimensions of thosecomponents. If the accuracy of the configurations and the dimensions ofthe inner ring raceway 14 a and of the small-diameter stepped portion 15among those elements are enhanced in the above relationship with thefitting surface, the perpendicularity of the fitting surface to therotational center of the hub 8 can be enhanced. Moreover, if removingthe thermal process deformation out of the fitting surface, the surfaceaccuracy of this fitting surface can also be enhanced.

A technology for preventing the deflection of the fitting flange 13which might conduce to the deflection of the rotor 2 may be what isdisclosed in, e.g., Japanese Patent Application Laid-Open PublicationNo. 10-217001. The prior art disclosed in this Publication does not,however, deal with anything about thermally processing the respectivecomponents, wherein the costs wastefully increase because of preciselyfinishing the surface which is not essentially needed as the fiducialsurface. While on the other hand, the inner ring raceway 14 a and thesmall-diameter stepped portion 15 are hardened over their surfaces andtherefore required to undergo the thermal process such as ahigh-frequency hardening process. Then, the configurations anddimensions of the inner ring raceway 14 a and the small-diameter steppedportion 15 might more or less change subsequent to the thermal process,and hence, according to the prior art disclosed in the abovePublication, it is difficult to sufficiently enhance the accuracy ofeach components in the way described above. Besides, the inventiondisclosed in the Publication given above takes a structure of fixing acouple of inner rings each separated from the hub to the outerperipheral surface of this hub, and therefore an error, etc. between theend surface of each inner ring and the inner ring raceway might be addedas an error of parallelism between the fitting surface of the fittingflange and the inner ring raceway. Furthermore, a contact portionbetween the hub and the inner ring is not worked based on the fittingsurface of the fitting flange, so that the parallelism between thefitting surface and the inner ring raceway is hard to sufficientlyenhance.

Moreover, the bearing unit 5 for the wheel and the rotor 2 have hithertobeen selectively combined in order to make offsets of the deflection ofthe fitting flange 13 and the deflection of the rotor 2 based on theconfiguration error of the rotor 2 itself. In this case, however, theselecting operation for the combination becomes laborious, resulting inan increase in cost.

SUMMARY OF THE INVENTION

It is a primary object of the present invention, which was devised undersuch circumstances, to improve a bearing unit for a wheel and amanufacturing method thereof.

To accomplish the above object, according to a first aspect of thepresent invention, a bearing unit for a wheel, comprises a static ringhaving a static-side raceway surface and fixedly supported by asuspension in a state of being used, a rotary ring having a rotary-sideraceway surface hardened by a thermal process, a plurality of rollingmembers provided between the rotary-side raceway surface and thestatic-side raceway surface, and a fitting flange, provided on an outerperipheral surface of the rotary ring, for fixedly joining a rotary bodyfor braking and a wheel to its side surface in a state of being used. Inthe thus constructed bearing unit for the wheel, the side surface of thefitting flange for fixedly joining the rotary body for braking and thewheel, is worked in a predetermined configuration after the rotary-sideraceway surface has been subjected to the thermal process, and therotary-side raceway surface is worked in a predetermined configurationand dimensions on the basis of the side surface of the fitting flange.

According to a second aspect of the present invention, a method ofmanufacturing a bearing unit for a wheel according to the first aspectof the invention, comprises a step of hardening a rotary-side racewaysurface of a rotary ring by a thermal process, a step of thereafterworking a side surface of a fitting flange in a predeterminedconfiguration, and a step of subsequently working the rotary-sideraceway surface in a predetermined configuration and dimensions by usingthe side surface of the fitting flange as a fiducial surface.

The bearing unit for the wheel according to the first aspect of theinvention and the manufacturing method according to the second aspect ofthe invention, are capable of making normal a relationship between therotary-side raceway surface and the side surface of the fitting flangeirrespective of deformations of the respective components which aresubsequent to a thermal process. As a result, it is feasible torestraining deflections of the rotary body for braking which is fixed tothe fitting flange by enhancing a perpendicularity of the side surfaceof the fitting flange to the rotational center of the rotary ring.

According to a third aspect of the present invention, a wheel bearingunit with a rotary body for braking, comprises a static ring having astatic-side raceway surface and fixedly supported by a suspension in astate of being used, a rotary ring having a rotary-side raceway surfacehardened by a thermal process, a plurality of rolling members providedbetween the rotary-side raceway surface and the static-side racewaysurface, a fitting flange provided on an outer peripheral surface of therotary ring, and a rotary body for braking such as a rotor or drum,fixedly joined to one single surface of the fitting flange and having abraked surface against which a frictional material is pressed whenbraking. In the thus constructed wheel bearing unit with the rotary bodyfor braking, the rotary-side raceway surface is worked in apredetermined configuration and dimensions on the basis of the brakedsurface of the rotary body for braking in a state where the rotary bodyfor braking is fixedly joined to the one single surface of the fittingflange.

According to a fourth aspect of the present invention, a method ofmanufacturing a wheel bearing unit with a rotary body for brakingaccording to the third aspect, comprises a step of hardening arotary-side raceway surface of a rotary ring by a thermal process, astep of thereafter fixedly joining the rotary body for braking to oneside surface of the fitting flange, and a step of subsequently workingthe rotary-side raceway surface in a predetermined configuration anddimensions by using the braked surface of the rotary body for braking asa fiducial surface.

According to a fifth aspect of the present invention, a wheel bearingunit with a rotary body for braking is constructed so that the brakedsurface of the rotary body for braking is worked in a predeterminedconfiguration and dimensions on the basis of a fitting surface of thestatic ring to the suspension.

According to a sixth aspect of the present invention, a method ofmanufacturing a wheel bearing unit with a rotary body for brakingaccording to the fifth aspect, comprises a step of hardening arotary-side raceway surface of a rotary ring by a thermal process, astep of thereafter effecting a finishing work on the rotary-side racewaysurface, a step of combining the rotary ring with the static ringthrough a plurality of rolling members, a step of fixedly joining therotary body for braking to a side surface of the fitting flange, and astep of subsequently working the braked surface of the rotary body forbraking in a predetermined configuration and dimensions by using thefitting surface of the static ring to the suspension as a fiducialsurface.

In the wheel bearing units each having the rotary body for braking andthe manufacturing methods thereof according to the third through sixthaspects, an assembling error between the fitting flange provided on theouter peripheral surface of the rotary ring and the fitting portion tothe rotary body for braking such as the rotor, does not lead to thedeflection of the braked surface of the rotary body for braking as inthe case of a decline of perpendicularity of the two side surfaces ofthe rotor and so on. Namely, in the case of the structures and themanufacturing methods according to the third through sixth aspects also,the rotary-side raceway surface (corresponding to the third and fourthaspects) or the braked surface (corresponding to the fifth and sixthaspects) is worked in the state where the rotary ring and the rotarybody for braking are joined as in the state of being used. Accordingly,the assembling error of the fitting portion exert no influence on thepositional relationship between the rotary-side raceway surface and thebraked surface, and there is no necessity for particularly enhancing theconfiguration accuracy of the members constituting the fitting portionand serving as a part of the fitting flange and of the rotary body forbraking.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing a first embodiment of the presentinvention:

FIG. 2 is a sectional view showing a state of working an outerperipheral surface of a hub in the first embodiment;

FIG. 3 is a sectional view showing a state of working the outerperipheral surface of the hub in a second embodiment;

FIG. 4 is a sectional view showing one example of assembling a bearingunit for a wheel, to which the present invention is applied;

FIG. 5 is a sectional view showing a state of working the outerperipheral surface of the hub in a third embodiment of the presentinvention;

FIG. 6 is a view taken along the arrow line A in FIG. 5;

FIG. 7 is a principal sectional view showing a fourth embodiment of thepresent invention;

FIG. 8 is a view taken along the arrow line B in FIG. 7; and

FIG. 9 is a sectional view showing a state of working two side surfacesof a rotor defined as a rotary body for braking in a fifth embodiment ofthe present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 and 2 show a first embodiment of the present invention. An outerperipheral surface of an outer ring 6 defined as a static ring isprovided with a joint flange 12 for fixedly joining the outer ring 6 toa knuckle 3 (FIG. 4). Outer ring double raceways 11 a, 11 b each servingas a static-side raceway surface are formed in an inner peripheralsurface of the outer ring 6 which is defined as a static-side peripheralsurface. A portion 6 a, indicated by lattice-hatching in an upper halfpart in FIG. 1 and embracing the outer ring raceways 11 a, 11 b, of theinner peripheral surface of an intermediate portion of the outer ring 6,is hardened over its entire periphery by high-frequency hardening.

Further, areas, facing to the outer ring raceways 11 a, 11 b, of outerperipheral surfaces of a hub 8 and an inner ring 16 which correspond toa rotary ring, are provided with inner ring raceways 14 a, 14 b eachserving as a rotary-side raceway surface. To be more specific, the innerring raceway 14 a is formed directly in an outer peripheral surface ofan intermediate portion of the hub 8, and the inner ring 16 having theinner ring raceway 14 b formed in its outer peripheral surface isfixedly fitted on a small-diameter stepped portion 15 formed at an innerside end of this hub 8. The inner ring 16 is composed of a hard metallike bearing steel such as SUJ2, and hardened to its core by thehardening process. Further, a fitting flange 13 for fixing a wheel 1constituting a traveling wheel and a rotor 2 (FIG. 4) classified as arotary body for braking or a drum, is provided at a portion closer tothe outer side end of the intermediate portion of the hub 8 andprotruding from an aperture of an outer side end of the outer ring 6.

Fitting holes 23 are respectively formed on the same circumference,concentric with a rotational center of the hub 8, in a plurality ofpositions in the circumferential direction of the fitting flange 13.Proximal ends of studs 24 are individually fixedly fitted in thesefitting holes 23. Each of the studs 24 includes a collar 25 provided ona proximal end surface thereof and a serrated portion 26 formed, closerto the proximal end, on the outer peripheral surface of the intermediateportion. The thus configured stud 24 is inserted outward from inward(from right to left in FIG. 1) into the fitting hole 23, and theserrated portion 26 is fitted by pressing into the fitting hole 23.Then, the collar 25 is made to impinge upon an inside surface of thefitting flange 13. Note that a widthwise central position of theserrated portion 26 which is indicated by a chain line α in FIG. 1 isset more inward than a thicknesswise central position of the fittingflange 13 which is indicated by a chain line β in FIG. 1 in a statewhere the stud 24 is fixed to the fitting flange 13 in the way describedabove. The following is an elucidation of the reason why so.

In this embodiment, an external surface 27 (a left side surface in FIGS.1 and 2) of the fitting flange 13 is set as a fitting surface to whichthe wheel 1 and the rotor 2 should be fitted. Accordingly, there must bea necessity for preventing a decline of configuration accuracy of theexternal surface 27 to the greatest possible degree. While on the otherhand, when the serrated portion 26 of the stud 24 is press-fitted intothe fitting hole 23, the fitting flange 13 might deform to some extentin the vicinity of the fitting hole 23. This deformation might extend tothe external surface 27, and, if the external surface 27 deforms in aconvex-direction, a deflection of the rotor 2 fixedly joined to thisexternal surface 27 tends to become large. Such being the case, thefitted portion between the fitting hole 23 and the serrated portion 26is set inward as much as possible, thereby preventing the externalsurface 27 from deforming in the convex-direction due to the deformationof the flange 13. As a matter of course, a width W₂₆ of the serratedportion 26 is set well smaller than a thickness T₁₃ of the fittingflange 13 (W₂₆<<T₁₃) within a range where a sufficient fitting strengthcan be ensured. In the illustrated embodiment, at the side end of thefitting hole 23, a chamfered large-diameter portion is formed in anaperture on the side of the external surface 27 by a counterboring workor lathe work. Hence, the convex-directional deformation of the externalsurface 27 due to the press-fitting of the serrated portion 26 can beprevented more surely. Further, though considered almost unnecessary, ifthe working on the external surface 27 is again performed after thepress-fitting of the serrated portion 26, the distortion of the externalsurface 27 can be eliminated with a certainty.

Moreover, as shown in FIGS. 5 and 6, an annular channel 123communicating with all the fitting holes 23 may be previously formed inthe external surface 27, thereby preventing the external surface 27 frombeing deformed and distorted based on the press-fitting of the serratedportion 26.

Further, the portion 8 a, indicated by the lattice-hatching in the upperhalf part in FIG. 1, of the outer peripheral surface of the hub 8 ishardened over its entire periphery by the high-frequency hardening. Ofthis hardened portion 8 a, the proximal end of the fitting flange 13 ishardened for preventing a plastic deformation of this proximal endirrespective of a large moment applied to the fitting flange 13 whentraveling. In addition, the inner ring raceway 14 a is hardened forpreventing an impression from being formed in the inner ring raceway 14a regardless of a large surface pressure applied to a contact areabetween balls 17, 17 which will hereinafter be explained. Further, thesmall-diameter stepped portion 15 is hardened for preventing thissmall-diameter stepped portion 15 from being plastically deformedirrespective of a large radial load applied from the inner ring 16.Moreover, a portion between the small-diameter stepped portion 15 andthe inner ring raceway 14 a is hardened for preventing this in-betweenportion from being plastically deformed regardless of a large momentload and thrust load applied when travelling.

A plurality of balls 17, 17 each defined as a rolling member areprovided in a state of being held by retainers 18, 18 between the outerring raceways 11 a, 11 b and the inner ring raceways 14 a, 14 b. Withthis configuration, the hub 8 is rotatably supported on the side of aninside diameter of the outer ring 6, and the traveling wheel includingthe wheel 1 and the rotor 2 can be rotatably supported with respect tothe knuckle 3. Note that seal rings 19 a, 19 b are provided between theinner peripheral surfaces of two side ends of the outer ring 6, theouter peripheral surface of the intermediate portion of the hub 8 andthe outer peripheral surface of the inner side end of the inner ring 16so as to cut off the space accommodating the balls 17, 17 from theoutside space, thereby preventing a leak of grease sealed in the abovespace and foreign matters from entering this space.

In the thus constructed bearing unit 5 for the wheel, the externalsurface 27 of the fitting flange 13, for fixedly joining the wheel 1 andthe rotor 2, is worked in the predetermined configuration after theouter peripheral surface 8 a, indicated by the lattice-hatching in theupper half part in FIG. 1, of the intermediate portion of the hub 8 hasbeen hardened by the high-frequency hardening process categorized as onetype of thermal processes. That is, the lattice-hatching portion 8 aundergoes the high-frequency thermal process and is thereby hardened.Then, the hub 8 comes to have a deformation based on the thermalprocess, and thereafter the outer periphery of the hub 8 as well as theexternal surface 27 are subjected to machining.

More in detail, the inner ring raceway 14 a formed directly in the outerperipheral surface of intermediate portion of the hub 8 and the outerperipheral surface and the stepped surface of the small-diameter steppedportion 15 formed at the inner side end of the hub 8, are worked inpredetermined configurations and predetermined dimensions on the basisof the external surface 27 as shown in FIG. 2, before or after theexternal surface 27 of the fitting flange 13 has been worked as the flatsurface by lathe turning or the like machining. Even before working theflange surface, the surfaces of the inner ring raceway 14 a and of thestepped portion 15 can be worked at by far higher accuracy than in theprior art because of the flange surface serving as the basis.

More specifically, a backing plate 28 abuts on the external surface 27and is joined to the fitting flange 13 by a magnetic attractive force,etc. then, the hub 8 is rotated by rotating the backing plate 28. Onthis occasion, a rotational center of the hub 8 is an axis orthogonal tothe external surface 27. Then, an unillustrated shoe is slid on theouter peripheral surface of the hub 8, and the inner ring raceway 14 aand the outer peripheral surface and the stepped surface of thesmall-diameter stepped portion 15 are, as indicated by broken lines inFIG. 2, machined in desired configuration as by cut working or precisionlathe working while being positioned in the radial direction of the hub8.

The machining described above is performed in such a way that the axisorthogonal to the external surface 27 serves as the rotational center.Hence, the positional relationship among the external surface 27, theinner ring raceway 14 a formed directly in the outer peripheral surfaceof the intermediate portion of the hub 8 and the inner ring raceway 14 bformed in the outer peripheral surface of the inner ring 16 (FIG. 1)fitted on the small-diameter stepped portion 15, becomes normalirrespective of the thermal deformation based on the high-frequencyhardening process described above. As a result, the deflection of theexternal surface 27 can be restrained down to a slight degree in a statewhere the wheel bearing unit 5 as illustrated in FIG. 1 is assembled.

Next, a second embodiment of the present invention will be shown in FIG.3. In accordance with the second embodiment, after an external surface27 of the fitting flange 13 provided on the outer peripheral surface ofthe hub 8 has been finished as a flat surface, in a state where theouter side end of the hub 8 is chucked by a chuck 30, the inner ringraceway 14 a formed directly in the outer peripheral surface of theintermediate portion of the hub 8 and the outer peripheral surface andthe stepped surface of the small-diameter stepped portion 15, are workedin predetermined configurations and dimensions. On this occasion, onesingle surface (a right end surface in FIG. 3) of the chuck 30 in theaxial direction abuts on the external surface 27, and the externalsurface 27 is used as a fiducial surface for working. Further, an innerperipheral surface of the chuck 30 is brought into contact with an outerperipheral surface of a cylindrical member 31 provided at the externalside end of the hub 8, thereby restraining a displacement in the radialdirection of the hub 8. In the second embodiment discussed above, it isfeasible to regulate more strictly the radial positions of the innerring raceway 14 a formed directly in the outer peripheral surface of theintermediate portion of the hub 8 and of the outer peripheral surface ofthe small-diameter stepped portion 15 formed at the inner side end ofthe hub 8. As a result, vibrations of the car when traveling can bedecreased by restraining the radial displacements of the wheel 1 and ofthe rotor 2 (FIG. 4). Other configurations and operations are the sameas those in the first embodiment, and hence the repetitive explanationsand illustrations of the same components are herein omitted.

FIGS. 7 and 8 show a fourth embodiment of the present invention. Notethat a feature of the present invention is a point of improving aperpendicularity of two side surfaces 130, 130 of the rotor 2 to thecentral axis α of the rotation of the hub 8 irrespective of anassembling error of the fitting portion between the fitting flangeprovided on the outer peripheral surface of the hub 8 and the rotor 2defined as the rotary body for braking. Other structures are the same asthose shown in FIG. 4 or in the embodiments discussed above, andtherefore the like components are omitted or simplified in terms oftheir explanations and illustrations. The following discussion will befocused on the characteristic elements of the present invention.

The rotor 2 classified as the rotary body for braking is joined by aplurality of studs 24 and a plurality of nuts 131 to the fitting flange13 provided at a portion closer to the outer side end of theintermediate portion of the hub 8 corresponding to a rotary ringtogether with the inner ring 16 (see FIG. 4). Further, the portion,indicated by lattice-hatching in the upper half part in FIG. 1, of theouter peripheral surface of the hub 8 is hardened over its entireperiphery by the high-frequency hardening process. Moreover, the twoside surfaces 130, 130 of the rotor 2 are worked in desiredconfigurations in the process of manufacturing the rotor 2. Morespecifically, those two side surfaces 130, 130 are paralleled to eachother as well as to two side surfaces of a joint flange 132 provided ata portion closer to the inner periphery in order to be fixedly joined tothe fitting flange 13. Parallelisms of the two side surfaces of thejoint flange 132 with respect to the above two side surfaces 130, 130may not be so precise.

In the way described above, the outer peripheral surface of the hub 8 ishardened, and the rotor 2 is fixedly joined to the fitting flange 13.Then, based on one of the two side surfaces 130, 130, the inner ringraceway 14 a formed directly in the outer peripheral surface of theintermediate portion of the hub 8 and the outer peripheral surface ofthe small-diameter stepped portion 15 and the stepped surface of thesame, are worked in the predetermined configurations and dimensions. Tobe specific, the backing plate 128 abuts on one (the outer side surfacein the illustrated embodiment) of the side surfaces 130, 130 of therotor 2, and is joined to the rotor 2 by the magnetic attractive force,etc. Subsequently, the hub 8 is rotated by rotating this backing plate128. On this occasion, the rotational center of the hub 8 is an axisorthogonal to the two side surfaces 130, 130 of the rotor 2. Then, ashoe 135 is slid on the outer peripheral surface of the hub 8, and theinner ring raceway 14 a and the outer peripheral surface of thesmall-diameter stepped portion 15 and the stepped surface of the sameare, as indicated by broken lines in FIG. 7, machined in desired surfaceconfiguration as by cut working or precision lathe working while beingpositioned in the radial direction of the hub 8. Incidentally, theposition where the shoe 135 is slid on the outer peripheral surface ofthe hub 8 is not limited to the position shown in FIG. 7 but may beproperly shifted such as on the outer peripheral surface of thesmall-diameter stepped portion 15 or the inner ring raceway 14 a. Inshort, the shoe 135 abuts upon a portion opposite in position in thediametrical direction to the portion where the machining is effected atthat point of time.

The machining described above is carried out, wherein the axisorthogonal to the two side surfaces 130, 130 of the rotor 2 serves asthe rotational center. Hence, the positional relationship among thosetwo side surfaces 130, 130, the inner ring raceway 14 a formed directlyin the outer peripheral surface of the intermediate portion of the hub 8and the inner ring raceway 14 b formed in the outer peripheral surfaceof the inner ring 16 (FIGS. 1 and 4) fitted on the small-diameterstepped portion 15, becomes normal irrespective of the thermaldeformation based on the high-frequency hardening process describedabove. As a result, the deflections of the two side surfaces 130, 130rotatably supported by the wheel bearing unit 5 as illustrated in FIG. 1can be restrained down to a slight degree in a state where the wheelbearing unit 5 is assembled.

Besides, the assembling error of the fitting portion between the jointflange 132 of the rotor 2 and the fitting flange 13 of the hub 8 exertsno influence upon the positional relationship between the inner ringraceway 14 a defined as a rotary-side raceway (as well as the inner ringraceway 14 b formed in the outer peripheral surface of the inner ring16) and the two side surfaces 130, 130 of the rotor 2 which may beconceived as braked surfaces (as far as the assembling error does notextremely worsen). Accordingly, there is no necessity for particularlyenhancing accuracy of the configurations of the joint flange 32 and ofthe fitting flange 13. As a consequence, it is feasible to restrain thecosts needed for minimizing the deflections of the two side surfaces130, 130 of the rotor 2.

Next, FIG. 9 shows a fifth embodiment of the present invention. Incontrast with the fourth embodiment discussed above, the fifthembodiment takes such a construction that the two side surfaces 130, 130of the rotor 2, which are the braked surfaces of the rotary body forbraking, are worked in predetermined configurations and dimensions onthe basis of a fitting surface, with respect to the knuckle 3 (see FIG.4) constituting a suspension, of the outer ring 6 defined as a staticring.

That is, in the fifth embodiment, to start with, the portion, includingthe inner ring raceway 14 a defined as the rotary-side raceway surface,of the hub 8 is hardened by the thermal process, and a finishing work iseffected on a necessary portion, inclusive of the inner ring raceway 14a, of the portion hardened by the thermal process. The hardening by thethermal process and the finishing work are performed by, e.g., themethod as described with reference to FIGS. 1 and 2 or 3. After thenecessary portion of the hub 8 has been thus worked, the hub 8 and theouter ring 6 as the static ring are combined through the plurality ofballs 17, 17 each serving as the rolling member, thereby constitutingthe wheel bearing unit 5. Thereafter, the rotor 2 as the rotary body forbraking is fixedly joined through the plurality of studs 24 and theplurality of nuts 131 to the external surface (an upper surface in FIG.9) of the fitting flange 13 provided on the outer peripheral surface ofthe hub 8. Note that a driving jig 133 for rotationally driving therotor 2 is, in addition to the rotor 2, fixedly joined to the externalsurface of the fitting flange 13 in the embodiment illustrated in FIG.9. This driving jig 133 is, as will hereinafter be described, after thetwo side surfaces 130, 130 of the rotor 2 have been subjected to thefinishing work, removed from the fitting flange 13. Note that thedriving jig 133 described above may not be fixedly joined to the rotor 2but can be detached therefrom by the magnetic attractive force, etc.

In any case, as explained above, after the fitting flange 13 has beenfixedly joined to the rotor in the way described above, the two sidesurfaces 130, 130 of the rotor 2 are worked in the predeterminedconfigurations and dimensions, wherein the fitting surface, to theknuckle 3 (FIG. 4) constituting the suspension, of the outer ring 6 isused as the fiducial surface. For attaining this, in accordance with thefifth embodiment, an inner side end (a lower side end in FIG. 9) of theouter ring 6 is fitted with no backlash into a support hole 140 formedin a support member 134, subsequently one single surface (a lowersurface in FIG. 9) of the joint flange 12 provided on the outerperipheral surface of the outer ring 6 abuts on the upper surface of thesupport member 134, and the joint flange 12 is fixedly joined through abolt 136 to the support member 134. Then, the hub 8 and the rotor 2 arerotationally driven by an unillustrated driving device through thedriving jig 133, and in the meantime the two side surfaces 130, 130 ofthe rotor 2 undergo the finishing work by use of tools 137, 137 such asprecision work cutting tools. As a matter of course, these tools 137,137 perform the finishing work of the two side surfaces 130, 130 whilemoving in parallel to the upper surface of the support member 134.

The wheel bearing unit 5 is manufactured by the methods as describedwith reference to FIG. 1, 2 or 3, and the external surface (the uppersurface in FIG. 9) of the fitting flange 13 exhibits a highperpendicularity to the rotational center of the hub 8. Further, agenerally known conventional technology might be sufficient for settingthe rotational center of the hub 8 concentric with the central axis ofthe outer ring 6 and ensuring the perpendicularity of the joint surface(the lower surface in FIG. 9) of the joint flange 12 with respect to thecentral axis of the outer ring 6. Accordingly, the parallelism of theexternal surface of the fitting flange 13 with the joint surface of thejoint flange 12 can be sufficiently obtained by combining the method asdescribed with reference to FIG. 1, 2 or 3, with the generally knownconventional technology. In addition, in the case of the fifthembodiment, as discussed above, the two side surfaces 130, 130 of therotor 2 undergo the finishing work while rotationally driving the hub 8and the rotor 2. It is therefore possible to ensure the sufficientparallelisms of the two side surfaces 130, 130 of the rotor 2 with thejoint surface of the joint flange 12 without enhancing especially theaccuracy of the configurations of the fitting flange 13 and of the jointflange 132 provided closer to the inner periphery of the rotor 2. As aresult, it is possible to minimize the costs required for restrainingthe deflections of the two side surfaces 130, 130 of the rotor 2 down tothe small level.

The wheel bearing unit with the rotary body for braking and themanufacturing method thereof according to the present invention, havethe above-described constructions and operations, and hence it isfeasible to restrain disagreeable noises and vibrations caused whenbraking without increasing particularly the costs.

1. A method of manufacturing a bearing unit for a wheel, including: astatic ring having a plurality of static raceway surfaces and supportedby a suspension in use; a rotary raceway ring having a plurality ofrotary raceway surfaces; a plurality of rolling members interposedbetween the static raceway surfaces and the corresponding rotary racewaysurfaces; and a fitting flange, having an internal surface and anexternal surface and provided on an outer peripheral surface of saidrotary ring, for fixedly joining said rotary body for braking and saidwheel to the external surface thereof in use, said method comprising:working the external surface of said fitting flange in a predeterminedconfiguration after an outer peripheral surface of an intermediateportion of said rotary ring has been hardened by a hardening process,but before the bearing unit is assembled as a unit.